External beam radiation therapy (EBRT) is one of the most commonly used treatments for numerous cancer types. In 2010, approximately 470,000 patients underwent radiation therapy (RT) in the US alone. Depending on their individual treatment plan, these patients may undergo between 1 and 70 separate RT visits over the course of several weeks. Although most RT treatments are performed accurately, accidents from equipment faults, failures in quality assurance methodologies, and errors during operation represent an unacceptable risk for both patients and healthcare providers. Recent reports indicate that between 0.6 and 4.7 incidents per 100 radiation therapy visits have been reported to occur even in advanced oncology centers operating with modern equipment and trained staff. However, these numbers may be grossly underestimated, as it is also widely recognized that many incidents remain unreported during RT. A significant number of these incidents occur during the delivery of RT and can result in underdosing or overdosing patients, irradiating healthy tissue, or, at worst, patient death. As EBRT techniques continue to increase in complexity, and with the increased use of stereotactic body radiotherapy (SBRT) and hypofractionation, there is a clear and growing need for a monitoring and validation methodology that enables clinicians to have greater confidence that they are delivering the planned dose where and how it was intended.
The standard of care for RT involves multiple steps, such as simulation, treatment planning, plan verification, patient setup, and treatment delivery. While numerous methods [e.g., in room lasers, tattoos on patient skin, mega- and kilovoltage (MV, kV) imaging, pretreatment dosimetry phantom studies, etc.] have been developed to ensure the fidelity of treatment delivery, there are no technologies currently available that are capable of fully monitoring treatment in the context of the patient's anatomy as it is being delivered.
In current practice, onboard MV electronic portal imaging (EPID) is utilized for monitoring the RT beam after it exits the patient. However, due to a lack of soft tissue contrast and multileaf collimator (MLC) blockage of the field of view, the available anatomic references provided by the approach are limited to bony anatomy or implanted fiducial markers that lie within the beam's eye view making the interpretation of the data nontrivial. More recently the potential of Cherenkov emission as a means of visualizing therapy in real time has been demonstrated. Also proposed was a method of utilizing air scintillation to visualize the radiation beam. While both seek to visualize therapeutic beam delivery, the signals generated are at least three orders of magnitude smaller than typical room lights. Thus, these techniques require long exposure times in darkened rooms or complex, expensive imaging setups to obtain usable measurements.
This poses a challenge to practical application. Therefore, the ability to visualize the position, shape, and intensity of the radiation beam as it passes through the patient in real time is not yet available in clinical practice.
What is needed is an imaging approach that can be readily implemented into existing RT treatment rooms and provide a means of monitoring beam shape, intensity and general location in real time.
Additionally, in the radiation therapy space, a great deal of effort is expended upon ensuring that medical sources of ionizing radiation operate properly. This is generally referred to as Quality Assurance (QA) and generally involves testing several aspects of the performance of the radiation therapy machines at regular intervals. Often these tests are time-consuming, tedious, and prone to operator error. Similar to the needs in monitoring therapy in real-time, there exists the need to perform quality assurance measurements with high temporal resolution and in an automated fashion.